Inkjet printing methods have simple printing processes, cost low, can produce multiple colors, can perform printing in an overlapping manner and obtain good print qualities because inkjet printing is contactless printing, and can perform high-speed printing without noise. Therefore, the inkjet printing methods are widely employed in home printers and commercial printers.
The inkjet printing methods perform printing by attaching low-viscosity inks on print media. Therefore, it is known that chromogenicity varies depending on fixing states of dyes included in the inks on print media.
When printing is performed using an ink set including a plurality of colors of inks including dyes as coloring materials, it is known that the coloring materials in the inks landing first on print media fix in surface layers of the print media, whereas that the coloring materials in the inks landing afterwards tend not to fix in the surface layers of the print media but fix in layers below the layers in which the coloring materials in the inks landing first have landed in the thickness direction of the print media.
Therefore, when bidirectional printing is performed using a plurality of colors of inks, there is a problem that the order in which the inks land on print media is different between the outward scanning printing and the homeward scanning printing to cause a color difference (bidirectional color difference) in the images formed.
Hence, there is provided an inkjet printing apparatus including a printing head provided with ink discharging ports symmetrically with respect to the main-scanning direction and configured to discharge inks in the outward scanning printing and in the homeward scanning printing in a manner that the inks land on print media in the same order to make it possible to obtain images having a small color difference due to bidirectional printing (see, e.g., PTL 1). There is also provided an inkjet printing head provided with discharging ports among which only discharging ports having a high ink discharging capacity are arranged symmetrically with respect to the main-scanning direction, to make it possible to obtain images having a small color difference due to bidirectional printing (see, e.g., PTL 2).